The present invention relates to a liquid-permeable topsheet for use in disposable body fluid absorptive articles such as sanitary napkins, disposable diapers and training pants.
In liquid-permeable topsheets used for body fluid absorptive articles, a technique is well known to make the topsheet from plastic film or nonwoven fabric, and to provide it with liquid passages each extending from top to bottom thereof. The upper surface of the sheet is in contact with the wearer's skin. Lower openings of the respective liquid passages so in contact with an absorbent core so that a capillary action occurring within each liquid passage may be utilized to transfer excreted body fluids toward the absorbent core.
Japanese Patent Publication No. 1982-17081 discloses a technique wherein a topsheet made of polyethylene film is provided with conically tapered capillaries having lower ends arranged to be in close contact with an absorbent core.
According to a technique disclosed by Japanese patent application Disclosure No. 1985-259261, a topsheet made of plastic film is provided with cylindrical liquid passages with their lower ends extending into an absorbent core. Such cylindrical liquid passages are more stable and therefore less deformable than conical liquid passages under a large load in the axial direction.
Japanese parent application Disclosure No. 1992-152945 discloses a technique according to which there is provided a high density area or rib continuously surrounding lower openings of respective liquid passages. This technique certainly stabilizes an opening of each liquid passage against deformation as well as collapse and allows the body fluids to be effectively transferred toward an absorbent core.
U.S. Pat. No. 4,741,941 discloses a method for making a topsheet provided with liquid passages utilizing the manufacturing process for melt blown nonwoven fabric or span bond nonwoven fabric. It is also proposed by this patent that woody pulp is fed onto the lower side of the topsheet and a combination thus integrated is used for absorptive articles.
Japanese patent application Disclosure No. 1981-11058 discloses a technique according to which an upper sheet made of hydrophobic material is integrally combined with a lower sheet made of hydrophilic material so that the lower sheet partially rises up through a layer of the upper sheet until it is exposed beyond the upper surface of the upper sheet and thereby a plurality of liquid-permeable spots are formed. According to this technique, the a foresaid liquid passages may be replaced by these liquid-permeable spots to introduce the body fluids toward an absorbent core.
The soft touch is generally essential to the topsheet and the conventional topsheets as disclosed by the above-identified Patent Publication and Disclosure are also made of thin and soft materials from such a viewpoint. With a negative consequence, however, the conical liquid passages disclosed by the Japanese Patent Publication No. 1982-17081 as well as the cylindrical liquid passages disclosed by the Japanese patent application Disclosure No. 1985-259261 are disadvantageous in that the lower openings, i.e., free ends of these liquid passages are liable to be deformed, so that the liquid passages readily collapse, for example, even under a relatively low pressure against the wearer and the body fluids are often prevented thereby from being smoothly transferred toward the absorbent core. While stability of each liquid passage against a compressive force axially exerted on the liquid passage can be more or less improved, the liquid passage is still easily collapsed under a force transversely exerted on the liquid passage since, after all, the liquid passage comprises soft material.
While the technique disclosed by the above-identified Japanese patent application Disclosure No. 1992-152945 may theoretically alleviate the problem of collapse, both a thickness of the topsheet and a diameter of the liquid passage are unfeasibly fine, i.e., it would not be easy to provide the previously mentioned high density area or rib continuously surrounding the lower openings of the respective liquid passages although this is one of the most important features of the disclosed technique.
The technique disclosed by U.S. Pat. No. 4,741,941 provides a soft cloth-like touch by using melt-blown nonwoven fabric, however such nonwoven fabric lacks firmness and consequently the liquid passages are liable to collapse and clog. In addition, the nonwoven fabric is in rather close contact with the pulp layer fed to and combined with the lower side of the nonwoven fabric and, when this combined material is used in the absorptive articles, a quantity of moisture once held by the pulp layer readily exudes and spreads over the upper surface of the melt-blown nonwoven fabric under body pressure of the wearer who experiences an unpleasant wetness.
The technique disclosed by Japanese patent application Disclosure No. 1981-11058 is free from apprehension that the liquid passages might be collapsed and clogged and the lower sheet visibly exposed through the upper sheet as viewed from above advantageously functions to absorb sweat when it comes in contact with the skin of the wearer, since the lower sheet is hydrophilic. However, the quantity of moisture once held by the lower sheet readily flows back toward the upper sheet under a body pressure of the wearer, since the lower sheet is in close contact with the upper sheet primarily composed of nonwoven fabric. Accordingly, this technique also has a problem that the wearer experiences an unpleasant feel of wetness.
In view of these unsolved prior art problems, it is a principal object of the invention to provide a topsheet comprising a first sheet having a skin-contacting area and a second sheet underlying said first sheet wherein said first sheet, is provided with liquid passages and said second sheet is welded to said first sheet around lower openings of the respective liquid passages so as to restrict possibly occurring deformation of the liquid passages, on the one hand, and spaced from the lower side of the skin-contacting area to avoid possibly occurring backflow of body fluids from the second sheet toward the first sheet, on the other hand, and thereby solve the problems encountered by the conventional topsheets.